Spiders, ants, wasps, and various insects are sometimes found in human living spaces. Various tools and techniques have been used to discourage their undesired presence and to stun or kill them to facilitate their removal, with mixed results. Pesticides and other chemical agents can be very effective, but may persist beyond the pests they are used against, sometimes with undesirable side effects. Traps may be ignored or avoided. Fly paper and other sticky surfaces can be effective traps, but may also be unsightly if one waits for multiple kills before disposing of them, and expensive if one disposes of them after each kill. Spiders and insects can be simply smashed against a wall or floor with a swatter, a shoe, a book, or another household object, but often some remains of the smashed pest are then left behind, smeared on the object that was used to kill the pest.